1. Field of the Invention
This invention relates to relatively high density ethylene polymers which are particularly suitable for blow molding and profile extrusion applications.
2. Information Disclosure Statement Including Description of Related Art
The following information is disclosed in accordance with the terms of 37 CFR 1.56, 1.97 and 1.98.
U.S. Pat. No. 4,336,352, issued Jun. 22, 1982 to Sakurai et al., and U.S. Pat. No. 4,525,322, issued Jun. 25, 1985 to Page et al., each discloses blow molding resin compositions composed of three ethylene polymers of different molecular weights, and states that such resins have satisfactory die swell as compared with compositions containing two ethylene polymers which are indicated to exhibit a less than satisfactory swell.
U.S. Pat. No. 4,603,173, issued Jul. 19, 1986 to Mack et al., discloses polyethylene blow molding resins obtained by lightly branching with free radical initiators compositions comprising two or three ethylene polymers of different molecular weights. The free radical initiator treatment is disclosed to be necessary to obtain a desired increase in the die swell of the resin composition.
U.S. Pat. No. 4,461,873, issued Jul. 24, 1984, and U.S. Pat. No. 4,547,551, issued Oct. 15, 1985, both to F. W. Bailey et al., each discloses blends of high molecular weight and low molecular weights ethylene polymers of purportedly narrow molecular weight distribution, useful in the production of films and blow-molded articles.
U.S. Pat. No. 4,048,412, issued Sep. 13, 1977 to Caumartin et al., discloses a process for the polymerization of olefins, e.g., ethylene, in a series of reaction vessels each operating in the gas phase and containing a fluidized bed of polymer and catalyst comprising a transition metal and organo-metallic compound as cocatalyst introduced into the first reactor, and wherein an additional amount of cocatalyst is introduced into a reactor other than the first. The patent discloses the use of different organoaluminum compounds as cocatalysts in the reactors for the purpose of varying the molecular weight distribution of the polymer.
U.S. Pat. No. 4,338,424, issued Jul. 6, 1982 to Morita et al., discloses a process for polymerizing olefins utilizing two gas phase polymerization zones, the first employing a higher hydrogen to olefin mole ratio to produce a low molecular weight (LMW) polymer and the second employing a lower hydrogen to olefin mole ratio to produce a high molecular weight (HMW) polymer. The process also includes a dilution zone between the two polymerization zones to which a fresh supply of olefin gas is added for feeding into the second polymerization zone.
U.S. Pat. No. 4,703,094, issued Oct. 27, 1987 to Raufast, discloses the production of polyolefins by the polymerization of alpha-olefins in the gas phase in several reactors, at least two of which are interconnected by a transfer device in which the gas mixture from the upstream reactor is subjected to decompression and compression stages, providing for elimination of the heat of reaction and degassing of the polymer powder.
U.S. Pat. No. 5,047,468, issued Sep. 10, 1991 to H. K. Lee et al., based on application filed Nov. 16, 1988, and corresponding European Published Patent Application No. 0 369 436, published May 23, 1990, disclose a process for the production of ethylene copolymers in the gas phase utilizing at least two fluidized bed reactors in series under conditions such that a high melt index copolymer is made in one reactor and a low melt index copolymer in the other. The disclosure states that the high and low melt index polymers can be made in any order. The catalyst employed is a complex of magnesium, titanium, a halogen, and an electron donor on an appropriate support such as a silica or alumina, in combination with an organoaluminum activator and co-catalyst.
U.S. Pat. No. 4,481,301, issued Nov. 6, 1984 to Nowlin et al., discloses catalysts for polymerizing alpha-olefins prepared by treating a support with an organo-magnesium compound and contacting the supported magnesium composition in a liquid medium with a tetravalent titanium compound.
Pending parent application Ser. No. 07/665,054, filed Mar. 6, 1991 (now abandoned), discloses a process for producing bimodal ethylene polymers in gas phase, fluidized bed, tandem reactors wherein a high molecular weight (HMW) polymer is produced in the first reactor and a low molecular weight (LMW) polymer is produced in the second reactor and deposited on the HMW particles from the first reactor. The process utilizes certain specifically defined reaction conditions and may employ one of the Ziegler catalysts contemplated for the preparation of the product of this invention. The entire disclosure of this application is incorporated by reference.
Pending application Ser. No. 07/712,283, filed Jun. 10, 1991 (now abandoned), discloses and claims catalysts for the control of the molecular weight distribution of ethylene polymers, prepared by impregnating with a dialkylmagnesium a slurry of a porous inorganic support having reactive --OH groups, in a non-polar solvent, treating the resulting intermediate with TiCl.sub.4, and reacting the Ti containing intermediate with an oxygen containing electron donor. Also disclosed and claimed is the use of the foregoing catalyst in a two stage gas phase tandem polymerization process in which a relatively high molecular weight (HMW) polymer is produced in a first reactor and transferred to a second reactor wherein a relatively low molecular weight (LMW) polymer is produced and combined with the HMW polymer.
Pending application Ser. No. 07/712,298, filed Jun. 10, 1991 (now abandoned), discloses and claims catalysts and their use in polymerization processes similar to those of Ser. No. 07/712,283 described in the preceding paragraph, except that in lieu of the reaction with an oxygen containing electron donor, the dialkylmagnesium-impregnated support is treated with a halogen containing reagent prior to the treatment with TiCl.sub.4.
Pending application Ser. No. 07/734,989, filed Jul. 24, 1991 (now abandoned), discloses high molecular weight, high density ethylene polymers which may be formed with good processability into films having improved mechanical properties, and which may be produced by a process employing gas phase, fluidized bed, tandem reactors.